test(sentinel): cover pubsub mapping on master change

Stubs PubSubProxy.changeNode and drives transform() with a synthetic
analyzed object to assert the mapped address is used on failover.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nkaradzhov

packages/client/lib/sentinel/index.ts

@@ -621,7 +621,7 @@ export default class RedisSentinel<
   }
 }
 
-class RedisSentinelInternal<
+export class RedisSentinelInternal<
   M extends RedisModules,
   F extends RedisFunctions,
   S extends RedisScripts,

packages/client/lib/sentinel/pub-sub-master-change.spec.ts

@@ -0,0 +1,54 @@
+import { strict as assert } from 'node:assert';
+import { describe, it, beforeEach, afterEach } from 'mocha';
+import sinon from 'sinon';
+import RedisClient from '../client';
+import { PubSubProxy } from './pub-sub-proxy';
+import { RedisSentinelInternal } from './index';
+
+describe('pubsub master change applies nodeAddressMap', () => {
+  const RAW_HOST = '10.0.0.99';
+  const RAW_PORT = 6390;
+  const MAPPED_HOST = 'external.example.com';
+  const MAPPED_PORT = 16390;
+
+  let changeNodeStub: sinon.SinonStub;
+  let clientConnectStub: sinon.SinonStub;
+  let internal: RedisSentinelInternal<{}, {}, {}, 2, {}>;
+
+  beforeEach(() => {
+    changeNodeStub = sinon.stub(PubSubProxy.prototype, 'changeNode').resolves();
+    clientConnectStub = sinon.stub(RedisClient.prototype, 'connect').resolves(undefined as any);
+
+    internal = new RedisSentinelInternal<{}, {}, {}, 2, {}>({
+      name: 'mymaster',
+      sentinelRootNodes: [{ host: '127.0.0.1', port: 26379 }],
+      nodeAddressMap: {
+        [`${RAW_HOST}:${RAW_PORT}`]: { host: MAPPED_HOST, port: MAPPED_PORT }
+      }
+    });
+    internal.on('error', () => { });
+  });
+
+  afterEach(() => {
+    changeNodeStub.restore();
+    clientConnectStub.restore();
+  });
+
+  it('passes the mapped address (not the raw sentinel-reported one) to PubSubProxy.changeNode', async () => {
+    await internal.transform({
+      sentinelList: [],
+      epoch: 0,
+      sentinelToOpen: undefined,
+      masterToOpen: { host: RAW_HOST, port: RAW_PORT },
+      replicasToClose: [],
+      replicasToOpen: new Map()
+    });
+
+    assert.equal(changeNodeStub.callCount, 1, 'PubSubProxy.changeNode should be called exactly once');
+    assert.deepEqual(
+      changeNodeStub.firstCall.args[0],
+      { host: MAPPED_HOST, port: MAPPED_PORT },
+      'pubsub proxy must reconnect to the mapped address after a sentinel failover'
+    );
+  });
+});